An instrument amplifier is an electronic amplifier that converts the inaudible electric or electronic signal from musical instruments such as an electric guitar, an electric bass, or an electric keyboard into sounds which can be heard by the performers and audience. Combination ("combo") amplifiers include a preamplifier, a power amplifier, and tone controls and one or more speakers in a wooden cabinet. Instrument amplifiers for some instruments are also available without an integral speaker.

Instrument amplifiers are available for specific instruments, including the electric guitar, electric bass, electric keyboards, and acoustic instruments such as the mandolin and banjo. Some amplifiers are designed for specific styles of music, such as the "traditional"-style "tweed" guitar amplifiers used by blues and country musicians, and the Marshall amplifiers used by hard rock and heavy metal bands.

Unlike home "hi-fi" amplifiers or public address systems, which are designed to accurately reproduce the source sound signals with as little harmonic distortion as possible, instrument amplifiers are often designed to add additional tonal coloration to the original signal or emphasize (or de-emphasize) certain frequencies. The two exceptions are keyboard amplifiers and "acoustic" instrument amplifiers, which typically aim for a relatively flat frequency response.